1. Field of the Invention
The present invention relates generally to the field of switch contacts and more particularly to an arrangement with improved fault-closing capability.
2. Description of the Related Art
When switch contacts of medium- and high-voltage switches are being closed, arcing may occur between the contacts either prior to or during initial contact engagement. The magnitude of the arcing is generally proportional to the available current in the circuit. The length of the arcing time is determined by factors such as voltage, the configuration of the contacts, and the speed of closing. Accordingly, in the presence of large currents (e.g., in the range of thousands of amperes) and/or long time durations, any resultant arcing and/or current flow during initial contact engagement can cause rather severe erosion of the contacts. Depending on the current level involved, one or more of such contact closings can result in impairment and reduction of the desirable current-carrying capacity of the switch contacts when the switch contacts are in their fully closed position with the contacts fully engaged. For example, the contact erosion can result in the absence of contact in the area of normal desired contact engagement when the contacts are in the fully closed position.
To limit and/or mitigate such contact erosion, the contacts may be provided with arcing tips or portions of arc-resistant material especially suited to avoid or minimize contact erosion; e.g., refractory material. For example, see U.S. Pat. No. 3,787,651. Of course, this adds to the complexity and cost of the manufacture of the contacts. Alternatively, an additional contact pair may be provided as a sacrificial contact pair to accommodate the arcing effects. However, this too results in a more complex and costly structure.
While the aforementioned arrangements may be generally suitable for their intended use, they do not efficiently provide for the accommodation of any arcing effects that result when two relatively movable contacts are closed.